A critical review of propulsion concepts for modern airships.

After a few decades in which airships have been depromoted to the level of being only considered as a mere curiosity they seem now to reappear. The main reasons for this are related to the recent progress in technology of materials, aerodynamics, energy and propulsion. Airships are also presenting themselves as green friendly air vehicles, in particular if solar powered airships are considered. Their ability to remain aloft for long time periods have also expanded the range of mission profiles for which they are suited. Herein we have concentrated on a critical overview of propulsion mechanisms for airships. These include a detailed overview of past, present, and future enabling technologies for airship propulsion. Diverse concepts are revisited and the link between the airship geometry and flight mechanics is made for diverse propulsion system mechanisms.